1. Field of the Invention
The present invention relates to thyristors, and is more particularly concerned with thyristors having plural control lines.
2. Description of the Prior Art
Thyristors which are used in self-commutating circuits, such as d.c. control elements, inverters, oscillating circuits etc, can be disconnected only by means of extinguishing circuits, the expense of which increases in accordance with the turn-off time. The thyristors are to exhibit a low turn-off time. For devices of systems operating at high frequencies, a short turn-off time is also necessary in order to safeguard the function of the device and to achieve a sufficiently favorable efficiency. A reduction in the turn-off time, by means of switching measures in the control circuit, permits the thyristors to be employed at a higher operating frequency and allows a reduction in the expense of the extinguishing function.
It is well known in the art to provide that thyristors having structures which serve to amplify the control current be supplied with an auxiliary voltage across the emitter electrode of the auxiliary thyristor in order to shorten the turn-off time, the plurality of such auxiliary voltage being opposed to that of the control voltage. This auxiliary voltage can be connected either permanently or only during the turn-off time. The auxiliary voltage serves to withdraw those charge carriers which are stored in the semiconductor body and which could otherwise trigger an ignition when the voltage subsequently increases in the blocking direction. Known realizations for the supply of the auxiliary voltage provide a diode which is arranged in the housing, or which is integrated in the semiconductor body of the thyristor, and which is connected to the auxiliary emitter electrode and the control terminal, and which is poled in such a manner that the control current for the thyristor cannot flow into the auxiliary emitter electrode.
However, these known structures require a control device to supply pulses of both polarities. The expense for the production of the negative auxiliary voltage can be kept lower for many applications, and in many cases it is advantageous if the auxiliary emitter electrode could be directly operated from the exterior, independently of the control electrode; for example, this facilitates the connection of a negative d.c. voltage which is easy to produce.